1. Field of the Invention
The present invention relates to a method and a system for monitoring exhaust gas recirculation. More particularly, the present invention relates to a method and a system for monitoring exhaust gas recirculation that can improve reliability of an EGR system in order to solve problems by accurately and rapidly monitoring an error of the EGR system.
2. Description of Related Art
Primary air pollutants of a diesel vehicle are nitrogen oxide (NOx) and particulate matter. Therefore, they become primary target matters for regulating exhaust gas of the diesel vehicle.
An exhaust gas recirculation (EGR) for reducing nitrogen oxide (NOx) has a characteristic of decreasing a combustion temperature by decreasing the density of an intake mixer without changing an air-fuel ratio of the mixer itself by making some of exhaust gas discharged after combustion contained in the intake mixer and flow into a combustion chamber.
That is, in the EGR device, in the case where emission such as NOx need be reduced according to an operation state of the engine, when some of the exhaust gas is provided to an intake through an EGR valve to flow into the combustion chamber together with the mixer, the volume of the exhaust gas that flows into the combustion chamber as inert gas is not changed. Therefore, the density of the mixer is relatively reduced, and as a result, a transmission speed of flames is reduced, thereby reducing a combustion speed. Accordingly, a combustion temperature is prevented from being raised to reduce the amount of generated emission such as NOx.
The EGR may be divided into a low-pressure EGR (LP EGR) system that recirculates exhaust gas passing through a turbine of a turbocharger through an intake passage at a front end of a compressor and a high-pressure EGR (HP EGR) that extracts exhaust gas between an exhaust manifold and the turbine and recirculates exhaust gas through the intake passage at a rear end of the compressor and an intercooler, as illustrated in FIG. 1.
It is monitored whether the high-pressure or low-pressure EGR system is erroneous by adopting two schemes in the related art.
That is, two schemes include an EGR monitoring scheme using a manifold absolute pressure sensor (MAP sensor) and an EGR monitoring scheme using a temperature sensor.
In the former scheme using the MAP sensor, a load variation is sensed by forcibly driving the EGR valve under a fuel supply interruption condition to sense a malfunction of the EGR device, and in the latter scheme using the temperature sensor, a temperature when the EGR valve operates is sensed by mounting the temperature sensor outside the EGR valve to sense the malfunction of the EGR device.
The scheme using the MAP sensor measures the amount of air that flows into an engine by detecting negative pressure of an intake manifold with electricity and thus is very sensitive to variation in electric resistance and cannot accurately sense a variation in the negative pressure depending on forcible driving of the EGR valve. The latter scheme using the temperature sensor senses the temperature of exhaust gas that passes through the EGR valve and thus has a problem that a response processing time is delayed and durability of the sensor itself deteriorates.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.